Growing concerns related to environmental sensitivity and ever increasing costs associated with all aspects of life in the twenty-first century form the basis for a never-ending search for replacements for current energy sources. The debate over availability of fossil fuels as a continuing energy source for electrical power production and for automotive fuels likely is made moot by volatility in production locations, price fluctuations, and increasing demand with a growing world population and increasing industrialization. Growing populations also further stress availability of sufficient nutrition worldwide, particularly when land-based food crops are displaced by crops intended for biofuel production (e.g., corn and sugar cane) as a possible replacement (or at least an extender) for fossil fuels.
To solve the foregoing problems in a society turning toward a philosophy of renewability, some have turned to algae as a possible fuel source. Simply stated, algae are photosynthetic organisms that use solar energy to combine water and carbon dioxide to produce organic materials, i.e., biomass. In general, there are two basic types of algae that are recognized in the field—microalgae and macroalgae. These two types of algae are distinctly different, botanically speaking, and have distinct characteristics, and hence usefulness, as biomass sources.
Microalgae (or microphytes) typically are recognized as unicellular species which exist individually or in chains or groups. Depending on the species, their sizes can range from a few micrometers to a few hundreds of micrometers. Unlike higher plants, microalgae do not have roots, stems, and leaves. Microalgae exhibit great biodiversity, and it has been estimated that about 200,000-800,000 species exist, of which about 35,000 species are described.
To date, research and development directed to fuel production using algae biomass has centered on microalgae as the algae of choice, typically because of the high oil content in many species of microalgae. Typically, research around the use of microalgae as a biomass source has focused on turning the microalgae into fuel or electrical energy via transesterification to biodiesel, fermentation to ethanol or methane, gasification to methane or hydrogen, pyrolysis to gas/liquid fuels, and burning to create heat or electricity. Many sources indicate that the creation of biodiesel from microalgae is the most promising use since subsidies on biodiesel are very high worldwide, and biodiesel is in general seen as a clean fuel. Also the process of producing diesel from biomass with lipids by transesterification is becoming well established. Methane production from microalgae is possible by fermentation, pyrolysis, or gasification but, at the present time, gasification typically is viewed as the most efficient process (because most of the biomass is converted into methane), although fermentation is cheaper to perform. To make microalgae a viable source of biomass, they must be produced in large volume, which has proven difficult. Ideal conditions for microalgae growth can be created in a laboratory; however, the costs to create these conditions are exceedingly high, and it is very difficult to scale up the laboratory environment efficiently.
There currently are two distinct methods being used for cultivation of microalgae. One method makes use of a raceway pond, which is a large open water raceway track where microalgae and nutrients are circulated around the pond track through use of a motorized paddle. With addition of carbon dioxide to the pond, it has been possible to grow microalgae, and the biggest advantage of these open ponds is their simplicity, yielding low production costs and low operating costs. Many algae species, however, cannot be grown in these ponds due to contamination, such as by other algae and bacteria. Also the process conditions, such as temperature and light, are hard or impossible to control.
The second method currently being used to grow microalgae is the photobioreactor. Unlike raceway ponds, this is a closed system with a controlled light source. Although use of the photobioreactor provides control over growth conditions, operation and production costs of photobioreactors are much higher due to the requirement for more complicated technology.
There are several advantages associated with the use of algae in general as a biomass energy source. For example, in many processes, converting algae biomass to energy can be substantially neutral with regard to carbon dioxide, and the fact that algae can use carbon dioxide and other flue gasses to grow has made them a growing subject of research. Furthermore, algae are a sustainable source of energy, and the basic requirements for algae growth (i.e., carbon dioxide, water, and sunlight) are available in abundance (particularly since freshwater is not necessarily required). Another advantage to use of algae is their highly efficient conversion of solar energy to biomass, particularly compared to typical land crops or trees. It is possible for algae to use almost 10% of the incoming sunlight for the photosynthesis process, and this can allow for a high biomass output per square meter per day. The problem in the art has been identifying all of the variables necessary to achieve a sustainable, high biomass output.
Widescale use of microalgae as a biomass source has been limited to date, and this primarily arises from the inability to grow mass cultures of microalgae at a competitive price. To earn maximum growth per square meter, a photobioreactor has been necessary, and such photobioreactors are extremely expensive compared to the traditional open pond systems. The open pool systems, however, have not been a viable option to date because it is hard, if not impossible, to control the growth process of the microalgae in the open environment. To date, only a few algae species have been identified as possible candidates for open pool growth systems because there are only a few species that lack detrimental sensitivity to contamination, and these species are often not the most efficient converters of sunlight and carbon dioxide to biomass. Besides the fact that growing algae is not economically viable at the moment, the conversion is not optimal as well. Because algae are wet they cannot be gasified without drying, which consumes a lot of energy and therefore lowers the overall efficiency. Supercritical water gasification has been proffered as a possible a solution, but it has not been successfully applied on a large scale. One extensive research initiative (see Golueke, C. and Oswald, W., 1968, “Power from Solar Energy via Algae-Produced Methane,” Solar Energy, 7(3), pp. 86-92) around conversion with fermentation arrived at the conclusion that 1.5 kWh of electrical energy per kg of algae could be produced by algae anaerobic fermentation and burning of the produced methane. With already established open pool growth rates of 10 grams/m2/hour, this would yield 15 W/m2, which means that the total electricity production of the Netherlands could be produced with 18,000 km2 of algae farms—about 45% of the total surface area of the Netherlands, which is of course not viable. These calculations only took into account the area needed to grow the algae, not the processing of the algae to methane. This represents only some of the problems to date associated with algae biomass production that is economically viable and technologically sound.
In a Position Paper by John R. Benemann (“Opportunities and Challenges in Algae Biofuels Production, September 2008), it was concluded that the cultivation of microalgae for biofuels in general and oil production in particular is not yet a commercial reality and, outside some niche, but significant, applications in wastewater treatment, still requires relatively long-term R&D, with emphasis currently more on the R rather than the D. Mr. Benemann states that this is due in part to the high costs of even simple algae production systems (e.g., open, unlined ponds), and in even larger part to the undeveloped nature of the required algal mass culture technology, from the selection and maintenance of algal strains in the cultivation systems, to achievement of high productivities of biomass with a high content of vegetable oils, or other biofuel precursors. Mr. Benemann also made the following observation. Assuming a currently achievable yield of about 50 metric tons per hectare per year biomass with 25% oil content (as triglycerides useful for biodiesel), or a yield of about 14,000 liters of oil per hectare per year, even assuming a $1/liter selling price, this would not be sufficient to cover the optimistic estimated capital costs (depreciation, return on capital, and other fixed costs), let alone any operating costs. He concludes that this clearly requires a major improvement in the productivity of such systems, with a doubling or even tripling in outputs of what is currently possible.
Considering all of the limitations associated with the potential use of microalgae as a biomass source, it is not surprising that macroalgae has not to date been given serious consideration as a possible biomass source. Specifically, it has been understood in the prevailing literature that macroalgae are not a reliable and useful biomass source. For example, macroalgae have been considered of little use because of the low macroalgae growth rate in comparison to the enormous short term growth rate of microalgae. Macroalgae also have been considered of little use because its low oil content relative to microalgae has hindered efficient production of oil derived biofuels.
Successfully growing algae of any type has been hindered to date because the rapidly growing algae are known to deplete the carbon dioxide in the growth medium (i.e., water), and this presents the requirement for supplementing the carbon dioxide from artificial sources to maintain growth rate. Disadvantages of algae use as a biomass source further are complicated by the difficulty and expense in separating algae from the aqueous growth medium and the difficulty and expense in separating the oil fraction from the algae. These and further shortcomings in the art are overcome by the present invention.